[clue-tech] NFS/server tuning with mail-ldap and maildirs

[Adam bultman]

Greetings.

A few questions for you cluesters out there:

I'm working on getting qmail-ldap, courier-imap/pop3 on serverblades, with NFS mounted maildirs.
However, when mailboxes get larger than a few thousand, things slow down a great deal, more than
 they should for a system like that.

The server will either spend time with imapd at about 10% usage, with it
waiting on the network, or imapd will take up ALL the cpu, and spin for
quite some time.

My configuration is this:

Netapp, with gigabit connection to the switch.

Server: 800 MHz serverblade, 512 MB RAM, 100Mbit connection to switch.

-
My plans are to use LVS and balance say, 3 to 4 servers from the 800 to
1200 MHz range handling mail services, with them all connecting to the
netapp back end via NFS.

But my fear is that people are going to have huge mailboxes, imapd will
sit for minutes on end, the users will get frustrated, and then complain.

Are there more effective NFS options for these servers to use?  Right
now, I'm using soft, noatime, tcp as my options. I don't know if using
TCP is any *faster*, or if setting the rsize or wsize will help any either.

Furthermore, should I be splitting up my services? The 1200 MHz systems
will have 1 G of ram instead of 512, should I use those for imap/pop
processing and the slower, 800 MHz systems for SMTP?

Any ideas would be most appreciated.  I'm wondering if there's a fundamnetal 
speed problem that I won't be able to overcome with more serverblades, or if
 there's other ways I could squeak more performance out of them.

Adam